System and method for using an output transformer for laser diode drivers

ABSTRACT

A laser diode driver output stage for driving an associated laser diode device. The laser diode driver output stage includes a driver circuit adapted to receive an input data signal at an input node and provide an output signal to a positive output node and a negative output node in response to the data signal. The laser diode driver output stage further includes a transformer having a positive terminal of a first side coupled to the positive output node of the driver circuit, a negative terminal of the first side coupled to the negative output node, a positive terminal of a second side coupled to the positive output node, and negative terminal of the second side coupled to a bias current generator. The transformer functions to isolate the bias current from fluctuations in the output signal, whereby the output signal and bias current are provided to the associated laser diode device.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an improved laser diode driverintegrated circuit, and in particular to a laser diode driver integratedcircuit having an improved output stage.

BACKGROUND OF THE INVENTION

A majority of laser diode driver integrated circuits (ICs) for opticaltransmission can be broadly divided into two categories. The firstcategory includes devices using direct modulation. This is generallyused for short distance transmission in which a laser diode driver IC isused to directly drive a laser diode module with a drive currentsupplied by the laser diode driver IC. The second category includesdevices which generally use external modulation. These are commonly usedfor long-distance transmission in which, for example, anelectroabsorption (EA) modulator driver IC is used to drive anelectroabsorption (EA) modulator module. In both of these categories,laser diode driver ICs can be found in both die forms in which the IC isassembled inside the laser module, and in packaged forms in which the ICis assembled outside of the laser module and connected by a transmissionline.

Due to the need for ever increasing data transmission rates, the use ofconventional laser diode driver integrated circuits results in numeroussignal quality problems. In addition, convention laser diode driverintegrated circuits consume a high amount of power due to the need forhigh supply voltages. Thus there is a need for laser diode driverintegrated circuits that provide improved output signal quality as wellas lower power consumption.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to a laser diodedriver output stage for driving an associated laser diode device. Thelaser diode driver output stage includes a driver circuit having atleast one input node, a positive output node, and a negative outputnode. The driver circuit is adapted to receive an input data signal atthe at least one input node and provide an output signal to at least oneof the positive output node and the negative output node in response tothe data signal. The laser diode driver output stage further includes atransformer having a positive terminal of a first side coupled to thepositive output node of the driver circuit, a negative terminal of thefirst side coupled to the negative output node, and a positive terminalof a second side coupled to the positive output node. The laser diodedriver output stage further includes a bias current generator coupled toa negative terminal of the second side of the transformer, the biascurrent generator providing a bias current to the negative terminal ofthe second side, and the transformer adapted to isolate the bias currentfrom fluctuations in the output signal, whereby the output signal andbias current are provided to the associated laser diode device.

Another embodiment of the present invention is directed to a method ofproviding an improved drive signal from a laser diode driver outputstage to a laser diode device, the method comprising the steps ofreceiving an input data signal at at least one input node of a drivercircuit, providing an positive output signal from the driver circuit toa positive output node in response to the data signal, and providing anegative output signal from the driver circuit to a negative output nodein response to the data signal. The method further includes the steps ofreceiving the positive output signal at a positive terminal of a firstside of a transformer and a positive terminal of a second side of thetransformer, receiving the negative output signal at a negative terminalof the first side of the transformer, and providing a bias current to anegative terminal of the second side of the transformer from a biascurrent generator. The method further includes the step of isolating thebias current from fluctuations in at least one of the positive outputsignal and the negative output signal, whereby the output signal andbias current are provided to the laser diode device.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the method and apparatus of the presentinvention may be obtained by reference to the following DetailedDescription when taken in conjunction with the accompanying Drawingswherein:

FIG. 1 illustrates an output stage of a conventional laser diode driverintegrated circuit (IC) and an associated laser diode;

FIG. 2 illustrates an output stage of a laser diode driver integratedcircuit (IC) in accordance with an embodiment of the present inventionand an associated laser diode;

FIG. 3 illustrates an output current eye diagram of a conventional laserdiode driver integrated circuit; and

FIG. 4 illustrates an output current eye diagram of laser diode driverintegrated circuit having a transformer and an RC network in the outputstage in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to the Drawings wherein like reference charactersdenote like or similar parts throughout the various Figures. Referringnow to FIG. 1, an output stage of a conventional laser diode driverintegrated circuit (IC) and associated laser diode is illustrated. Theoutput of a conventional laser diode driver IC 102 is connected to alaser diode 104. The conventional laser diode driver IC 102 includes aconventional laser diode driver integrated circuit output stage 106therein.

The conventional laser diode driver integrated circuit output stage 106comprises a pre-driver circuit 108 and a conventional driver circuit110. During operation, the pre-driver circuit 108 provides differentialinput data signals (IN+,IN−), representative of the data signal that isdesired to be transmitted by the laser diode 104, to the conventionaldriver circuit 110. In response to the differential input data signals(IN+,IN−), the conventional driver circuit 110 provides a modulatedoutput drive signal to the laser diode 104, which generates an opticaloutput data signal that is representative of the differential input datasignals (IN+,IN−).

The conventional driver circuit 110 of the conventional laser diodedriver integrated circuit output stage 106 typically comprises an outputswitch architecture in the form of a bipolar junction transistor (BJT)differential pair configuration. The conventional driver circuit 110 ofFIG. 1 includes a first transistor 112 and second transistor 114 whoserespective emitter nodes are joined together and biased by a modulationcurrent source 116 providing a modulation current (Imod), which isfurther connected to a low reference supply voltage (Vee). The collectornode of the first transistor 112 is connected to a negative outputterminal 118 of the conventional laser diode driver IC 102 through adummy diode 128. The negative output terminal 118 is further connectedto high reference supply voltage (Vcc) through a connection having awire bond inductance 132. The collector node of the second transistor114 is connected to a positive output terminal 120 through a dampingresistor 122.

The conventional driver circuit 110 further includes a bias currentsource 124 for providing a bias current (Ibias) to a bias current outputterminal 126. In addition, the bias current source 124 possesses aparasitic capacitance 130 that acts in parallel to the bias currentsource 124. The bias current source 124 is further connected to the lowreference supply voltage (Vee). The function of the bias current (Ibias)is to push the laser diode 104 operating range beyond its thresholdvalue and into the linear region of operation.

An anode of the laser diode 104 is connected to the high referencesupply voltage (Vcc), while a cathode of the laser diode 104 isconnected to the positive output terminal 120 through a connectionhaving a wire bond inductance 134. In addition, the laser diode 104inherently possesses a parasitic capacitance which is shown by acapacitor 136. This parasitic capacitance may be on the order of severalpicofarads (pF). The cathode of the laser diode 104 is normally furtherconnected to the bias current output terminal 126 through a ferrite bead138 functioning as an isolator.

During operation, the aforementioned differential input data signals(IN+,IN−) are provided from the pre-driver circuit 108 to the respectivegate nodes of the first transistor 112 and the second transistor 114.The modulation current source 116 provides the modulation current (Imod)that is modulated in proportion to the transmitted data signal, whilethe bias current source 124 provides the bias current (Ibias) to biasthe laser diode 104 just prior to oscillation. In response to thedifferential input data signals (IN+,IN−), the differential pairconfiguration provides the modulated output drive signal to the negativeoutput terminal 118 and the positive output terminal 120 for driving thelaser diode 104.

In order to drive a laser diode 104 to transmit data at higher rates,for example, a rate of 10 Gbits/sec or greater, a modulation current of60 mA, and a bias current of 60 mA is typically necessary. In addition,it is necessary for the output current falling time/rising time (tr/tf)transition to be at as high a rate as possible, typically on the orderof 20-30 picoseconds (ps).

In order to handle the high current requirements and the high speedpulse requirements, the conventional laser diode driver IC 102 isusually packaged inside a laser module driver in a die form, and wirebonded onto the laser diode 104. When packaged in this form and with theaforementioned drive requirements, the wire bond inductance 132, 134 andparasitic capacitance 136 of the laser diode 104, causes ringing on theoutput current waveform with a frequency approximately equal to the bitrate of data transmission. As a consequence of this ringing, a largeamount of overshoot/undershoot, small eye opening of the eye diagram,and an increase in deterministic jitter is present.

The aforementioned damping resistor 122, typically having a value ofseveral ohms to several tens of ohms, functions to suppress suchringing. However, the damping resistor 122 causes degradation of therising time/falling time (tr/tf) of the output current waveform, as wellas a shortage of headroom of the second transistor 114 when used at lowsupply voltages. The ferrite bead 138, placed between the positiveoutput terminal 120 and the bias current output terminal 126, acts as anisolator between fluctuations in the modulation current and the biascurrent. Without the ferrite bead 138, the parasitic capacitance 130 ofthe bias current source 124 will fluctuate due to the ringing generatedin the modulation current waveform as a result of wire bond inductances.The fluctuation in the parasitic capacitance 130 results in fluctuationsin the bias current (Ibias), which causes further degradation of theoutput current waveform.

The conventional laser diode driver integrated circuit output stage 106of FIG. 1 possesses several disadvantages. At high data transfer rates,such as at bit rates greater than 10 Gbits/sec, the parasiticcapacitance and inductance of ferrite bead 138 impacts the opticalcharacteristics of the laser diode 104. In addition, it is desirablefrom a packaging standpoint to have both the output switch stage andbias current source 124 inside the integrated circuit package.

When the power supply voltage is at a high level, e.g. greater than 5volts, the output switch stage and bias current source 124 can beisolated by cascading the bias current source 124. However, with a lowpower supply voltage, e.g. 3.3 volts this is difficult to achieve, as itis difficult to meet both the requirement for a large drive current(more than 60 mA) and adequate collector-emitter voltage headroom whenthe bias current circuit is configured with bipolar transistors.

Referring now to FIG. 2, an output stage of a laser diode driverintegrated circuit (IC) in accordance with an embodiment of the presentinvention and an associated laser diode is illustrated. The laser diodedriver IC 202 is connected to a laser diode 104 for providing amodulated output drive signal. The laser diode driver IC 202 includes alaser diode driver integrated circuit (IC) output stage 206 thatincludes a pre-driver circuit 208 and a driver circuit 210 comprised ofan output switch architecture. In the presently described embodiment,the driver circuit 210 of the laser diode driver integrated circuitoutput stage 206 comprises a bipolar conjunction transistor (BJT)differential pair configuration functioning as a differential amplifier.

The driver circuit 210 of FIG. 2 includes a first switch transistor 212and a second switch transistor 214 whose respective emitter nodes arejoined together and biased by a modulation current source 216 provided amodulation current (Imod). The modulation current source 216 is furtherconnected to a low reference supply voltage (Vee). The collector node ofthe first switch transistor 212 is connected to a negative outputterminal 218 of the laser diode driver IC 102 through a dummy diode 228.The negative output terminal 218 is further connected to high referencesupply voltage (Vcc) through a connection. This connection will have aninherent wire bond inductance 132. The collector node of the secondswitch transistor 214 is connected to a positive output terminal 220.

The driver circuit 210 further includes a bias current source 224 forproviding a bias current (Ibias) whose function is to push the laserdiode 104 operating range beyond its threshold value and into the linearregion of operation. The bias current source 224 possesses a parasiticcapacitance 230 that acts in parallel to the bias current source 224.

In accordance with the present invention, a transformer 232 is connectedwithin the integrated circuit output stage 206. It should be understoodthat the transformer 232 may be comprised of an on-chip transformerfabricated on the die of the laser diode driver integrated circuitoutput stage 206. Alternately, the transformer 232 may be comprised ofany other suitable transformer either external to or internal to theintegrated circuit package.

Still referring to FIG. 2, a negative terminal of a primary side (Lp) ofthe transformer 232 is connected to the collector node of the firstswitch transistor 212 through an RC network 238, and a positive terminalof the primary side (Lp) of the transformer 232 is connected to thecollector node of the second switch transistor 214. In the presentembodiment, the RC network 238 is comprised of a capacitor 240 andresistor 242 connected in series, although it should be understood thatany suitable RC network can be used. A positive terminal of a secondaryside (Ls) of the transformer 232 is connected to the collector node ofthe second switch transistor 214, and a negative terminal of thesecondary side (Ls) of the transformer 232 is connected to the biascurrent source 224. The bias current source 224 is further connected tothe low reference supply voltage (Vee).

Further, a primary side resistor 234 is connected in parallel betweenthe positive and negative terminals of the primary side (Lp) of thetransformer 232, and a secondary side resistor 236 is connected inparallel between the positive and negative terminals of a secondary side(Ls) of the transformer 232.

The anode of the laser diode 104 is connected to the high referencesupply voltage (Vcc), while the cathode of the laser diode 104 isconnected to the positive output terminal 220 through a connectionhaving a wire bond inductance 134. In addition, the laser diode 104possesses a parasitic capacitance 136 of several picofarads (pF).

During operation, differential input data signals (IN+,IN−) are providedfrom the pre-driver circuit 208 to the respective gate nodes of thefirst switch transistor 212 and the second switch transistor 214. Themodulation current source 216 provides the modulation current (Imod)that is modulated in proportion to the transmitted data signal, whilethe bias current source 224 provides a bias current (Ibias) to bias thelaser diode 104. In response to the differential input data signals(IN+,IN−), the differential pair configuration provides a modulatedoutput drive signal to the negative output terminal 218 and the positiveoutput terminal 220 for driving the laser diode 104.

During the driving of the laser diode 104, an output current, comprisedof the modulation current and bias current (Imod+Ibias), is output fromthe positive output terminal 220. Due to the parasitic capacitance 136of the laser diode 104 and the wire bond inductance 134 at the positiveoutput terminal 220, ringing occurs at the edges of the output currentwaveform.

The use of the transformer 232 and RC network 238 between the positiveand negative sides of the output switch in accordance with theprinciples of the present invention produces a transient current flow inthe opposite direction of the ringing of the output current waveform.This results in a decrease in the rising times/falling times (tr/tf) ofthe output current waveform transitions. In addition, the tr/tftransition edge of the transient current generates an electromotiveforce (Vip) on the primary side of the transformer 232, resulting in asuppression of the ringing in the output current waveform. It should beunderstood, that the characteristics of the transient current can beadjusted by an appropriate choice of the network time constant of the RCnetwork 238, which enables adjustment of the overshoot/undershoot causedby the output current tr/tf and ringing.

The transformer 232 and RC network 238 of the present invention alsoprovides for improved isolation of the bias current from output currentwaveform fluctuations. When current is fed to the laser diode 104,transient current flowing through the RC network 238 results in the edgeof the rising time/falling time (tr/tf) waveform transitions generatingan electromotive force Vip on the primary side (Lp) of the transformer232. As a result of the electromotive force Vip, a correspondingelectromotive force Vis is generated at the secondary side (Ls) of thetransformer 232 connected to the bias current source 224 in proportionto the coupling factor K of the transformer 232. The resultantelectromotive force Vis is generated in the inverse direction as that ofthe abrupt transition of the waveform at the positive output terminal220. As a result of the generation of the electromotive force Vip,fluctuation of the parasitic capacitance 230 of the bias current source224 caused by the output current waveform is suppressed.

The secondary side resistor 236, placed in series with the secondaryside of the transformer 232 and the bias current source 224, functionsas a damping resistor to suppress ringing generated by the parasiticcapacitance 230 of the bias current source 224 and the inductance of thesecondary side (Ls) of the transformer 232.

It should be understood that numerous modifications may be made to theembodiment of FIG. 2 without departing from the spirit of the presentinvention. Although the invention of FIG. 2 is illustrated using abipolar junction transistor (BJT) pair architecture as a driver circuit,any other suitable output switch architecture may be used, such as thoseusing field effect transistors (FETs), CMOS devices, etc. In addition,although the driver circuit of FIG. 2 is illustrated through the use ofa single stage emitter-coupled differential amplifier, a multi-stagedifferential amplifier having a transformer in its output stage may beused without departing from the spirit of the invention. The principlesof the present invention are also applicable to output stages havingboth single-ended and differential outputs and/or inputs.

Although the embodiment of FIG. 2 illustrates the use of a laser diodedriver IC to drive a laser diode, the principles of the presentinvention are equally applicable to an electroabsorption (EA) modulatordriver IC used to drive an electroabsorption (EA) modulator module forlong distance transmission. Additionally, the principles of the presentinvention are applicable to any driver device used to drive a load.

Referring now to FIG. 3, an output current eye diagram of a conventionallaser diode driver integrated circuit is illustrated. As illustrated inFIG. 3, a large amount of ringing and current fluctuation is present inthe output current signal. FIG. 4 illustrates an output current eyediagram of laser diode driver integrated circuit having a transformerand an RC network in the output stage in accordance with the principlesof the present invention. As can be seen in FIG. 4, ringing and currentfluctuation in the output current signal has been greatly reduced.

The improved laser diode driver integrated circuit output stage of thepresent invention provides several benefits over conventional laserdiode driver integrated circuits. The laser diode driver IC of thepresent invention allows for a lower supply voltage (e.g. Vcc=3.3Vtypical) over that of a conventional laser diode driver IC, resulting inlower power consumption. In addition, output current ringing caused byparasitic capacitance of the laser diode and the wire bond inductance ofthe output pad can be greatly reduced without resulting in an increasein the rising times and the falling times of the output waveformtransitions. Additionally, a reduction in the deterministic jitter andeye opening in the eye diagram of the output current is achieved.

The present invention provides for the further benefit of reducing theimpact of the output current switch stage generating the modulationcurrent upon the bias current source generating the bias current, evenwhen the output switch stage and the bias current source are connectedwithin the integrated circuit.

Although a preferred embodiment of the method and apparatus of thepresent invention has been illustrated in the accompanying Drawings anddescribed in the foregoing Detailed Description, it is understood thatthe invention is not limited to the embodiment disclosed, but is capableof numerous rearrangements, modifications, and substitutions withoutdeparting from the spirit of the invention as set forth and defined bythe following claims.

1. A laser diode driver output stage for driving an associated laserdiode device, the laser diode driver output stage comprising: a drivercircuit having at least one input node, a positive output node, and anegative output node, the driver circuit adapted to receive an inputdata signal at the at least one input node and provide an output signalto at least one of the positive output node and the negative output nodein response to the data signal; a transformer having a positive terminalof a first side coupled to the positive output node of the drivercircuit, a negative terminal of the first side coupled to the negativeoutput node, and a positive terminal of a second side coupled to thepositive output node; an RC network coupled between the negative outputnode of the driver circuit and the negative terminal of the first sideof the transformer, the RC network adapted to suppress ringing of theoutput signal from the positive output node; and a bias currentgenerator coupled to a negative terminal of the second side of thetransformer, the bias current generator adapted to provide a biascurrent to the negative terminal of the second side, the transformeradapted to isolate the bias current from fluctuations in the outputsignal, whereby the output signal and bias current are provided to theassociated laser diode device.
 2. The laser diode driver output stage ofclaim 1, wherein the first side of the transformer comprises a primaryside, and the second side of the transformer comprises a secondary side.3. The laser diode driver output stage of claim 1, wherein the ringingof the output signal is caused by at least one of a parasiticcapacitance of the laser diode device and a wire bond inductance at thepositive output node of the driver circuit.
 4. The laser diode driveroutput stage of claim 1, further comprising: a first side resistorcoupled in parallel between the positive terminal of the first side ofthe transformer and the negative terminal of the first side of thetransformer.
 5. The laser diode driver output stage of claim 1, furthercomprising: a second side resistor coupled in parallel between thepositive terminal of the second side of the transformer and the negativeterminal of the second side of the transformer, the second side resistoradapted to suppress ringing generated by at least one of a parasiticcapacitance of the bias current generator and an inductance of thesecond side of the transformer.
 6. The laser diode driver output stageof claim 1, wherein the driver circuit comprises an output switcharchitecture.
 7. The laser diode driver output stage of claim 1, whereinthe driver circuit comprises a differential amplifier.
 8. The laserdiode driver output stage of claim 1, wherein the driver circuitcomprises: a first switch transistor adapted to receive a firstdifferential input data signal of the input data signal at a first gatenode; and a second switch transistor adapted to receive a seconddifferential input data signal of the input data signal at a second gatenode, wherein a first emitter node of the first switch transistor iscoupled to a second emitter node of the second switch transistor, afirst collector node of the first switch transistor is coupled thenegative output node, and a second collector node of the second switchtransistor is adapted to provide the output signal to the positiveoutput node.
 9. The laser diode driver output stage of claim 8, furthercomprising a modulation current generator coupled to the first emitternode and the second emitter node.
 10. The laser diode driver outputstage of claim 1, further comprising a pre-driver circuit adapted toprovide the input data signal to the driver circuit.
 11. A laser diodedriver output stage for driving an associated laser diode device, thelaser diode driver output stage comprising: a driver circuit having atleast one input node, a positive output node, and a negative outputnode, the driver circuit adapted to receive an input data signal at theat least one input node and provide an output signal to at least one ofthe positive output node and the negative output node in response to thedata signal; a transformer having a positive terminal of a first sidecoupled to the positive output node of the driver circuit, a negativeterminal of the first side coupled to the negative output node, and apositive terminal of a second side coupled to the positive output node;and a bias current generator coupled to a negative terminal of thesecond side of the transformer, the bias current generator providing abias current to the negative terminal of the second side, thetransformer adapted to isolate the bias current from fluctuations in theoutput signal, whereby the output signal and bias current are providedto the associated laser diode device.
 12. The laser diode driver outputstage of claim 11, wherein the first side of the transformer comprises aprimary side, and the second side of the transformer comprises asecondary side.
 13. The laser diode driver output stage of claim 11,further comprising: an RC network coupled between the negative outputnode of the driver circuit and the negative terminal of the first sideof the transformer, the RC network adapted to suppress ringing of theoutput signal from the positive output node.
 14. The laser diode driveroutput stage of claim 13, wherein the ringing of the output signal iscaused by at least one of a parasitic capacitance of the laser diodedevice and a wire bond inductance at the positive output node of thedriver circuit.
 15. The laser diode driver output stage of claim 11,further comprising: a first side resistor coupled in parallel betweenthe positive terminal of the first side of the transformer and thenegative terminal of the first side of the transformer.
 16. The laserdiode driver output stage of claim 11, further comprising: a second sideresistor coupled in parallel between the positive terminal of the secondside of the transformer and the negative terminal of the second side ofthe transformer, the second side resistor adapted to suppress ringinggenerated by at least one of a parasitic capacitance of the bias currentgenerator and an inductance of the second side of the transformer. 17.The laser diode driver output stage of claim 11, wherein the drivercircuit comprises an output switch architecture.
 18. The laser diodedriver output stage of claim 11, wherein the driver circuit comprises adifferential amplifier.
 19. The laser diode driver output stage of claim11, wherein the driver circuit comprises: a first switch transistoradapted to receive a first differential input data signal of the inputdata signal at a first gate node; and a second switch transistor adaptedto receive a second differential input data signal of the input datasignal at a second gate node, wherein a first emitter node of the firstswitch transistor is coupled to a second emitter node of the secondswitch transistor, a first collector node of the first switch transistoris coupled the negative output node, and a second collector node of thesecond switch transistor is adapted to provide the output signal to thepositive output node.
 20. The laser diode driver output stage of claim19, wherein the first switch transistor comprises a first bipolarjunction transistor, and the second switch transistor comprises a secondbipolar junction transistor.
 21. The laser diode driver output stage ofclaim 19, further comprising a modulation current generator coupled tothe first emitter node and the second emitter node.
 22. The laser diodedriver output stage of claim 11, further comprising a pre-driver circuitadapted to provide the input data signal to the driver circuit.
 23. Amethod of providing an improved drive signal from a laser diode driveroutput stage to a laser diode device, the method comprising the stepsof: receiving an input data signal at at least one input node of adriver circuit; providing an positive output signal from the drivercircuit to a positive output node in response to the data signal;providing a negative output signal from the driver circuit to a negativeoutput node in response to the data signal; receiving the positiveoutput signal at a positive terminal of a first side of a transformerand a positive terminal of a second side of the transformer; receivingthe negative output signal at a negative terminal of the first side ofthe transformer; providing a bias current to a negative terminal of thesecond side of the transformer from a bias current generator; andisolating the bias current from fluctuations in at least one of thepositive output signal and the negative output signal, whereby theoutput signal and bias current are provided to the laser diode device.24. The method of claim 23, wherein the first side of the transformercomprises a primary side, and the second side of the transformercomprises a secondary side.
 25. The method of claim 23, furthercomprising the step of: suppressing ringing of the positive outputsignal from the positive output node using an RC network coupled betweenthe negative output node of the driver circuit and the negative terminalof the first side of the transformer.
 26. The method of claim 25,wherein the ringing of the positive output signal is caused by at leastone of a parasitic capacitance of the laser diode device and a wire bondinductance at the positive output node of the driver circuit.
 27. Themethod of claim 23, further comprising the step of: suppressing ringinggenerated by at least one of a parasitic capacitance of the bias currentgenerator and an inductance of the second side of the transformer bycoupling a side resistor in parallel between the positive terminal ofthe second side of the transformer and the negative terminal of thesecond side of the transformer.
 28. A driver output stage for driving anassociated device, the driver output stage comprising: a driver circuithaving at least one input node, a positive output node, and a negativeoutput node, the driver circuit adapted to receive an input data signalat the at least one input node and provide an output signal to at leastone of the positive output node and the negative output node in responseto the data signal; a transformer having a positive terminal of a firstside coupled to the positive output node of the driver circuit, anegative terminal of the first side coupled to the negative output node,and a positive terminal of a second side coupled to the positive outputnode; and a bias current generator coupled to a negative terminal of thesecond side of the transformer, the bias current generator providing abias current to the negative terminal of the second side, thetransformer adapted to isolate the bias current from fluctuations in theoutput signal, whereby the output signal and bias current are providedto the associated device.
 29. The driver output stage of claim 28,wherein the first side of the transformer comprises a primary side, andthe second side of the transformer comprises a secondary side.
 30. Thedriver output stage of claim 28, further comprising: an RC networkcoupled between the negative output node of the driver circuit and thenegative terminal of the first side of the transformer, the RC networkadapted to suppress ringing of the output signal from the positiveoutput node.
 31. The driver output stage of claim 30, wherein theringing of the output signal is caused by at least one of a parasiticcapacitance of the associated device and a wire bond inductance at thepositive output node of the driver circuit.
 32. The driver output stageof claim 28, further comprising: a first side resistor coupled inparallel between the positive terminal of the first side of thetransformer and the negative terminal of the first side of thetransformer.
 33. The driver output stage of claim 28, furthercomprising: a second side resistor coupled in parallel between thepositive terminal of the second side of the transformer and the negativeterminal of the second side of the transformer, the second side resistoradapted to suppress ringing generated by at least one of a parasiticcapacitance of the bias current generator and an inductance of thesecond side of the transformer.
 34. The driver output stage of claim 28,wherein the driver circuit comprises an output switch architecture. 35.The driver output stage of claim 28, wherein the driver circuitcomprises a differential amplifier.
 36. The driver output stage of claim28, wherein the driver circuit comprises: a first switch transistoradapted to receive a first differential input data signal of the inputdata signal at a first gate node; and a second switch transistor adaptedto receive a second differential input data signal of the input datasignal at a second gate node, wherein a first emitter node of the firstswitch transistor is coupled to a second emitter node of the secondswitch transistor, a first collector node of the first switch transistoris coupled the negative output node, and a second collector node of thesecond switch transistor is adapted to provide the output signal to thepositive output node.
 37. The driver output stage of claim 36, whereinthe first switch transistor comprises a first bipolar junctiontransistor, and the second switch transistor comprises a second bipolarjunction transistor.
 38. The driver output stage of claim 36, furthercomprising a modulation current generator coupled to the first emitternode and the second emitter node.
 39. The driver output stage of claim28, further comprising a pre-driver circuit adapted to provide the inputdata signal to the driver circuit.
 40. The driver output stage of claim28, wherein the driver output stage comprises a laser diode driveroutput stage.
 41. The driver output stage of claim 28, wherein thedriver output stage comprises an electroabsorption modulator driveroutput stage.